In a typical fixing apparatus, such as a copying machine, a piece of copy paper having an unfixed toner picture adhered thereto is passed between rubber heating and pressing rollers to fix the toner picture to the copy paper. However, numerous problems are associated with the use of conventional rubber fixing rollers which are commonly coated with a fluorocarbon resin. Because the resin has no elasticity, the heating roller tends to crush the toner, thereby lowering the picture quality of the copy. Lack of elasticity also lowers the heat conductivity of the roller resulting in poor toner fixing, a particular problem in high-speed copying machines. A roller that lacks elasticity also tends to wrinkle the copy paper.
A heating roller coated with a heat-resistant rubber also creates problems in the copying process. The separating pawls of the copying machine often damage the rubber coating when a copier becomes jammed with paper, thereby shortening roller life. Further, such a roller has poor toner releasing properties which tends to offset the toner and, thus, lower the picture quality of the copy.
Unexamined Japanese Patent Publication No. 60-179770 [hereinafter referred to as the Japanese Publication], filed by the same applicant herein, discloses improving the useful life of rubber rollers by using a rubber layer of porous ethylene tetrafluoride resin impregnated with liquid silicone rubber.
The roller disclosed in the Japanese Publication, however, also has problems associated with its use. One such problem concerns the rubber hardness which cannot be made with less than a Shore hardness of 50 degrees and, consequently, is too high. Also, because of polishing, the roller surface has uneven portions of several micrometers resulting in reduced toner releasing properties, particularly when the roller is used for color copying and like processes. In that case, the roller preferably has a mirrored surface to produce a glossy picture. Furthermore, when a porous material such as ethylene tetrafluoride resin is used to coat the roller, it is impossible to impregnate the pores of the material with a liquid rubber having a high viscosity (10,000 c.s. or more) generally used in a liquid injection molding system (LIMS). This is because the pore diameter is very fine, about 20 .mu.m at the most, which limits the quantity of filler that can be used to improve the copying characteristics of the roller.